The present invention relates to a rotary switch and more specifically to a miniature rotary switch assembly which is most suited for installation on a circuit board. Recently, there has been a strong demand in the market for a miniature rotary switch of this sort.
A prior art rotary switch disclosed in Japanese provisional utility model publications Nos. 149339, 149340/1984 has a rotor rotatably held in a cavity formed by a housing and a case. On the under surface of the rotor is disposed a contact with a pattern which wipably touches by turn on any one of contact projections of a contact member positioned between the rotor and the housing upon the rotation of the rotor whereby at least one of the fixed contact elements of the terminal leads on the housing is electrically connected with a contact projection of the contact member.
As shown in FIGS. 12 through 15, a rotary switch of the prior art disclosed in the Japanese provisional publications listed above has a housing 91 provided with terminal pins 92, 93, 94, 95 and 96 insertably moulded therein. The ends of the terminal pins 92-96 are exposed on the surface of the housing 91 as illustrated by hatched portions and define fixed contacts 97, 98, 99, 100 and 101 to which are respectively assigned one of the values 1, 2, 4, 8 of the binary number system or the decimal number system.
It should be noted that the numerals 96 and 101 represent a common terminal pin and a common fixed contact respectively.
A piece of contact member 102 which is composed of a square planar conductive metal plate carries a plurality of contact fingers 102.sub.1, 102.sub.2, 102.sub.3, 102.sub.4, and 102.sub.5, numeral 102.sub.3 being a common contact finger facing to a common fixed contact 101.
The contact fingers 102.sub.1 -102.sub.5 extend alternately in opposite directions as shown in FIG. 15. For example, the contact finger 102.sub.1 extends to the right while the contact finger 102.sub.2 extends to the left in FIG. 15. The same directional arrangement exists between the finger 102.sub.3 and the finger 102.sub.4. The contact fingers 102.sub.1, 102.sub.2, 102.sub.3, 102.sub.4 and 102.sub.5 are spaced from and opposed to fixed contacts 97, 98, 101, 99 and 100 of terminal pins 92-96 respectively leaving a small clearance therebetween.
Upon the middle surface of the contact fingers 102.sub.1,-102.sub.5 are positioned projections 102.sub.6 respectively. These projections 102.sub.6 are insertably held in holes h defined in a holder plate 107 positioned unmovably underneath a rotor 104.
The holder plate 107 helps to keep each contact member 102 at its set position by preventing undesirable shifting thereof by means of holes h which hold the projections 102.sub.6 of contact fingers 102.sub.1 -102.sub.5 therethrough.
As is shown in FIG. 12, a case 103 is fitted to the housing 91 to form a cavity C therebetween and the rotor 104 is rotatably held captive therein. As heretofore explained the holder plate 107 is arranged unmovably between the undersurface of the rotor 104 and the upper surface of the housing 91. A slot 104.sub.2 is defined in the middle surface of the rotor head 104.sub.1. The rotor 104 is rotated, by for example the rotation of a screw driver or the like engaged in the slot 104.sub.2.
An O-ring 105 is positioned in a clearance formed between the case 103 and the rotor 104 thereby to prevent undesired material (e.g. dust or grease) from passing inwardly toward the cavity C.
On the undersurface of the rotor 104 is arranged a cam pattern 110 provided with a circumferential cam 108 (as indicated by hatched portions) concentric with a center groove 109 of the rotor 104 and with a plurality of tapered cams 104.sub.4 having tampered sections 104.sub.6 and 104.sub.7 and a top projections 104.sub.5 as illustrated by hatched portions which are disposed along the periphery of the rotor 104.
Upon the rotation of the rotor 104, the cam pattern 110 rotates therewith. The circumferential cam 108 continuously and wipably touches on the projection 102.sub.6 disposed on the common contact finger 102.sub.3 whereby an electrical connection between the common terminal pin 96 and the common finger contact 102.sub.3 of the contact member 102 is continuously performed, while a plurality of tapered cams 104.sub.4 touch on the projections 102.sub.6 disposed on the finger contact 102.sub.1, 102.sub.2, 102.sub.4 and 102.sub.5 in seriatim whereby an electrical connection between the terminal pins 97, 98, 99 and 100 and the finger contacts 102.sub.1, 102.sub.2, 102.sub.4, 102.sub.5 are performed respectively.
The prior art contact member 102 is square in shape and provided with contact fingers 102.sub.1, 102.sub.2, 102.sub.3, 102.sub.4, 102.sub.5 alternately and oppositely arranged facing fixed contacts 97-101 of terminal pins 92-96 leaving a small clearnace therebetween. In order to maintain the contact fingers 102.sub.1 -102.sub.5 at their set positions, the holder plate 107 positioned underneath the rotor 104 is provided such that the projection 102.sub.6 of the contact fingers 102.sub.1 -102.sub.5 are insertably held by the holes h defined therein to keep the contact member 102 at its set position.